1. Technical Field
The present invention relates generally to an improved method to manage logical volumes and, in particular, to a method and an apparatus for managing a multi-layer logical volume management environment. Still more particularly, the present invention provides a method and an apparatus to order features dynamically and to resolve conflicts in the multi-layer logical volume management environment.
2. Description of the Related Art
The Logical Volume Manager (LVM) is a subsystem for on-line disk storage management that adds an additional layer between the physical devices and the block I/O interface in the kernel of the operating system to allow a logical view on storage. For systems without an LVM, each of the partitions that is usable by the operating system is assigned a drive letter, such as xe2x80x9cC:xe2x80x9d or xe2x80x9cF:xe2x80x9d, producing a correlating drive letter for each partition on a disk in the computer system. The process which assigns these letters is commonly known.
For systems with an LVM, a drive letter may be mapped instead to a logical volume which may contain one or more partitions. The process by which partitions are combined into a single entity is known generically as xe2x80x9caggregation.xe2x80x9d
There are various forms of aggregation, such as Drive Linking and software Redundant Array of Independent Disks (xe2x80x9cRAIDxe2x80x9d). Each feature, i.e. a function that may be performed on a partition, aggregate or volume, offered by the LVM for use on a volume is a layer in the LVM. The input to a layer has the same form and structure as the output from a layer. The layers being used on a volume form a stack, and I/O requests are processed from the top most layer down the stack to the bottom most layer. Typically, the bottom most layer is a special layer called the Pass Through layer.
U.S. patent application Ser. No. 09/561,184, abandoned, which is hereby incorporated by reference, discloses a multi-layer logical volume management system for an LVM in the OS/2 operating system. Similar systems can be extended to handle multiple levels of aggregation in other operating systems.
Multiple levels of aggregation allows multiple aggregators, such as Drive Linking and software RAID, to be used together to bypass the limitations inherent in each individual aggregation technology. As an example, many software RAID implementations have a limit on the number of partitions that can be combined into a single entity. However, by using Drive Linking to combine several software RAID entities into a single volume, the volume can have the benefits of software RAID while employing more partitions than software RAID by itself would allow.
A multi-layer logical volume management system introduces complexity and new management issues, such as ordering of features and management of conflicts when two or more features require the same position in a hierarchy. Therefore, it would be advantageous to have a method and an apparatus to manage the various features in a multi-layer logical volume management system.
The present invention provides a method and apparatus to dynamically order features and resolve conflicts in a logical volume management environment. The method and apparatus classifies features of a logical volume into partition level, aggregate level and volume level classes. Based on these classes and the attributes associated with each feature, ordering of the features in a feature stack is performed and conflicts between features identified for conflict resolution. In addition, the apparatus and method provides a mechanism by which a default ordering of features selected by a user may be generated for a logical volume. The user may accept this default ordering or edit the ordering as long as the user does not generate any conflicts. Any conflicts generated will be reported to the user and the attempted ordering will not be allowed.